Method for molding products made from metal or plastic materials

ABSTRACT

A method for molding products made from metal materials is provided, which includes the following steps: heating a metal material to a melting temperature; and quenching the metal material from the melting temperature to a quenching temperature. The quenching temperature being 5˜20 degrees centigrade lower than room temperature. A method for molding products made from plastic materials is also provided, which includes the following steps: heating a plastic material to a melting temperature; decreasing temperature from the melting temperature to a glass transition temperature of the plastic material; quenching the plastic material from the glass transition temperature to a quenching temperature, with the quenching temperature being 5˜20 degrees centigrade lower than room temperature; tempering the plastic material from the quenching temperature to a tempering temperature; and decreasing temperature from tempering temperature to room temperature.

TECHNICAL FIELD

The present invention relates to methods for molding products, inparticular, to a method for molding products made from metal or plasticmaterials.

BACKGROUND

With the great development of technologies, market competition in thefield of consumer electronic products becomes furious. Formanufacturers, in order to sell out their products, efforts have beenfocused not only on functions of the products, but also on appearance ofthe products.

A shell of commonly used consumer electronic products is often made ofmetal or plastic materials. Shells with crude and tarnished surface willaffect the appearance of the products. In addition, since shells areoften touched by customers' hands, wear resistant properties areimportant to influence the appearance. Besides, impact resistantproperties of shells are also important, which can prevent theappearance of the products from being destroyed by sudden impact orfall.

To improve surface properties of shells, particular treatment should beprovided. Typically, heat treatments, such as quenching or tempering arewidely used. While, during quenching, the shell will be naturally cooleddown to room temperature. Sizes of crystal grains of the shells formedtherefrom usually become large, whereby the surfaces of the shellsbecome rough. This will not only influence brightness and smoothness ofthe surface, but also affect the toughness of the shell.

Therefore, a heretofore-unaddressed need exists in the industry toaddress the aforementioned deficiencies and inadequacies.

SUMMARY

In a first preferred embodiment, a method for molding products made frommetal materials includes the following steps: heating a metal materialto a melting temperature; and quenching the metal material from themelting temperature to a quenching temperature. The quenchingtemperature is 5˜20 degrees centigrade lower than room temperature.

In a second preferred embodiment, a method for molding products madefrom plastic materials includes the following steps: heating a plasticmaterial to a melting temperature; decreasing the temperature from themelting temperature to a glass transition temperature of the plasticmaterial; quenching the plastic material from the glass transitiontemperature to a quenching temperature; tempering the plastic materialfrom the quenching temperature to a tempering temperature; anddecreasing the temperature from the tempering temperature to roomtemperature. The quenching temperature is 5˜20 degrees centigrade lowerthan room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the molding methods can be better understood withreference to the following drawings.

FIG. 1 is a temperature—time graph of a method for molding products madefrom metals of a first preferred embodiment;

FIG. 2 is a flow chart of the method of FIG. 1;

FIG. 3 is a temperature—time graph of a method for molding products madefrom plastics of a second preferred embodiment; and

FIG. 4 is a flow chart of the method of FIG. 3.

DETAILED DESCRIPTION

A method of a first preferred embodiment is used for molding a metalshell. During dead-end molding step, temperature alteration of the metalshell should be controlled strictly as the method described, so as toget improved mechanical properties on a surface layer of metal products.Referring to FIGS. 1 and 2, T₁ represents a melting temperature of themetal. T_(R) represents room temperature. T_(q) represents a quenchingtemperature. First of all, when a metal shell raw product is made, metalmaterial on surface layer of the metal shell row product is heated tothe melting temperature (T₁) thereof. After maintaining the temperatureat the melting temperature (T₁) for 10˜20 seconds, the melted metal isquenched rapidly from the melting temperature (T₁) to the quenchingtemperature (T_(q)). The quenching temperature (T_(q)) is 5˜20 degreescentigrade lower than room temperature (T_(R)). During this process,quenching rate from the melting temperature to the quenching temperatureshould be controlled fast, normally at a rate of 5˜100 degreescentigrade per second, preferably 20˜50 degrees centigrade per second.In order to prevent the metal shell from crisp, it is preferable tomaintain the temperature at the quenching temperature for a long time,e.g., for about half-hour. Thus, finished metal product is manufactured.

During this process, the metal shell is treated with rapid quenchingtechnology. Since the quenching rate is fast, and the quenchingtemperature is lower than room temperature, there's no time for grainsof the metal material growing by diffusion mechanism. Thus sizes ofcrystal grains of the metals will be reduced, surface roughness will bedecreased and brightness will be enhanced. Accordingly, compared withnature cooling process, the quenching process of the preferredembodiment could get a smaller grain size.

The metal materials which are suitable to the above rapid quenchingprocess is selected from the following group comprising of aluminiummagnesium alloy, magnesium aluminium alloy, aluminium magnesium titaniumalloy, aluminium magnesium chromium alloy, iron carbon alloy, stainlesssteel, magnesium alloy and titanium molybdenum alloy.

A method of a second preferred embodiment is used for molding plasticshell, before a injection molding step. This method includes thefollowing steps: heating a plastic material to a melting temperaturethereof; decreasing the temperature from the melting temperature to aglass transition temperature thereof; dwelling or keeping pressure atthe glass transition temperature; quenching the plastic material fromthe glass transition temperature to a quenching temperature; first heatinsulating or keeping temperature at the quenching temperature;tempering the plastic material from the quenching temperature to atempering temperature; second heat insulating at the temperingtemperature; and decreasing the temperature from the temperingtemperature to room temperature. Referring to FIGS. 3 and 4, T₂represents the glass transition temperature of the plastic. T_(R)represents room temperature. T_(q) represents the quenching temperature.T_(a) represents the tempering temperature.

When manufacturing, plastic particles are firstly fed into a chamber ofan injection-molding machine, and then heated to melt at a meltingtemperature. The melting temperature of a plastic is normally about 300degrees centigrade, at which the plastic is flowable. Thus the meltedplastics can flow from the chamber to a runner, and then into a cavity.When the cavity is filled with melted plastic material, decreasing thetemperature from the melting temperature to the glass transitiontemperature (T₂) of the plastic material. During that step, the plasticmaterial changes from a glassy state to a rubbery state. To differentplastics, the melting temperature and the glass transition temperatureare different. The glass transition temperature of plastics is normallyabout 100 degrees centigrade. In order to prevent plastic material fromstrong shrinkage due to sudden quencher, a dwell step is preferred,during that step, at the glass transition temperature, pressure in thecavity is maintained for about 10 seconds, referring to the firststraight line in FIG. 2. Then quenching the glassy stated plasticmaterial rapidly from the glass transition temperature (T₂) to thequenching temperature (T_(q)) at a quenching rate of 5˜100 degreescentigrade per second, preferably 2˜50 degrees centigrade per second.The quenching temperature is 5˜20 degrees centigrade lower than roomtemperature (T_(R)).

After maintaining temperature at the quenching temperature (T_(q)) for10˜20 seconds, the plastic material undergoes a tempering step, that is,the temperature rises rapidly from the quenching temperature (T_(q)) toa tempering temperature (T_(a)) with a rising rate of 5˜80 degreescentigrade per second, preferably 10˜40 degrees centigrade per second.And then after maintaining temperature at the tempering temperature for20˜60 seconds, the temperature is decreased rapidly to room temperatureat a decreasing rate of 10˜20 degrees centigrade per second. Finally,followed with a rejection molding process, a plastic shell is formed.

Furthermore, in order to prevent melted plastic material from oxidating,during rapid quenching step and/or rapid tempering step, protectivegases are introduced, which could be chosen from inert gases, such asnitrogen, argon or helium.

The plastic materials could be a composite material, such as aacrylonitrile butadiene styrene (ABS) resin added with fiberglass. Theplastic could be used in mobile phone, notebook, desktop computer, DVD,liquid crystal display et al.

During molding of products made of metal or plastic materials, a rapidquenching process and/or a rapid tempering process are applied. Sincethe quenching rate is fast, quenching temperature is lower than roomtemperature, there is no time for the sizes of crystal grains ofplastics growing at a diffusion mechanism. Thus sizes of crystal grainsof the plastics will be reduced, furthermore, brightness, smoothness andsurface toughness will be enhanced.

For metal alloy or plastic, particle size is an important factor whichcan affect fracture toughness of the materials. Fracture toughness(K_(1c)) is one of main mechanical parameters for metal alloy orplastic. Fracture toughness indicates an ability of the material forpreventing micro crack extension. Generally, when the fracture toughnessis high, the material exhibits a good mechanical property. The fracturetoughness satisfies the following formula:${\left. K_{1c} \right.\sim\sigma_{y}} \cdot \left( \frac{3.14159c}{d} \right)^{0.5}$wherein K_(1c) represents fracture toughnesss; σ_(y) represents yieldstrength, also known as yield limit; c represents crack length; and drepresents particle size. It can be deducted from the above formula thatthe smaller the particle size, the larger the fracture toughness. Thus,when quenching at the temperature of lower than room temperature, sizesof crystal grains are reduced, thus fracture toughness will be enhanced.

In order to further improve the brightness of the shells made frommetals or plastics, phosphorus or nano luminous materials could be addedinto the metals or the plastics. These nano luminous materials could bechosen from the following: ZnS, CdSe, CdS, Eu—ZnSiO_(x), Eu—YBO₃ andEu—BaMgAlO_(x).

It is believed that the present embodiments and their advantages will beunderstood from the foregoing description, and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the invention or sacrificing all of its materialadvantages, the examples hereinbefore described merely being preferredor exemplary embodiments of the invention.

1. A method for molding products made from metal materials comprises thefollowing steps: heating a metal material to a melting temperature; andquenching the metal material from the melting temperature to a quenchingtemperature, with the quenching temperature being 5˜20 degreescentigrade lower than room temperature.
 2. The method as claimed inclaim 1, wherein a quenching rate of quenching step is 5˜100 degreescentigrade per second.
 3. The method as claimed in claim 2, wherein thequenching rate is 20˜50 degrees centigrade per second.
 4. The method asclaimed in claim 1, wherein the metal materials are chosen from thefollowing group: aluminium magnesium alloy, magnesium aluminium alloy,aluminium magnesium titanium alloy, aluminium magnesium chromium alloy,iron carbon alloy, stainless steel, magnesium alloy and titaniummolybdenum alloy.
 5. The method as claimed in claim 4, wherein the metalmaterials further comprises nano luminous materials, chosen from thefollowing group: ZnS, CdSe, CdS, Eu—ZnSiO_(x), Eu—YBO₃ andEu—BaMgAlO_(x).
 6. A method for molding products made from plasticmaterials comprises the following steps: heating a plastic material to amelting temperature; decreasing the temperature from the meltingtemperature to a glass transition temperature of the plastic material;quenching the plastic material from the glass transition temperature toa quenching temperature, with the quenching temperature being 5˜20degrees centigrade lower than room temperature; tempering the plasticmaterial from the quenching temperature to a tempering temperature; anddecreasing temperature from tempering temperature to room temperature.7. The method as claimed in claim 6, wherein a quenching rate from glasstransition temperature to the quenching temperature is 5˜100 degreescentigrade per second.
 8. The method as claimed in claim 7, wherein thequenching rate is 20˜50 degrees centigrade per second.
 9. The method asclaimed in claim 6, wherein the tempering temperature is 80˜100 degreescentigrade.
 10. The method as claimed in claim 6, wherein a temperingrate from the quenching temperature to the tempering temperature is 5˜80degrees centigrade per second.
 11. The method as claimed in claim 10,wherein the tempering rate is 20˜50 degrees centigrade per second. 12.The method as claimed in claim 6, further comprising a step ofprocessing a dwell step for 10 seconds after decreasing to the glasstransition temperature.
 13. The method as claimed in claim 6, whereinafter decreasing to quenching temperature, maintain temperature at thequenching temperature for 10˜20 seconds.
 14. The method as claimed inclaim 6, wherein when rising to tempering temperature, maintaintemperature at the tempering temperature for 20˜60 seconds.
 15. Themethod as claimed in claim 6, wherein the plastic materials are ABSresin added with glass fiber.
 16. The method as claimed in claim 1,wherein during quenching step and/or tempering step, inert gases areintroduced.
 17. The method as claimed in claim 6, wherein duringquenching step and/or tempering step, inert gases are introduced.